A hollow core body for signal transmission cable 600 shown in FIG. 5 is known in the art (See, for example, Patent Documents 1 and 2). This hollow core body for signal transmission cable 600 includes an inner conductor 16 and a hollow insulating core 60. The inner conductor 16 includes a twisted conductor formed by bunching and twisting plural strands 6, 6, . . . . The hollow insulating core 60 includes an inner annular member 61 that surrounds the inner conductor 16, plural rib members 62 that radially extend from the inner annular member 61, an outer annular member 63 that couples outer ends of the rib members 62, and plural hollow members 64 that are enclosed by the inner annular member 61, the rib members 62, and, the outer annular member 63.